1. Field of the Invention
The present invention relates to a thin film magnetic head.
2. Discussion of Background
Most thin film magnetic heads employed in magnetic disk devices constituting computer storage apparatuses at present are the combined type that are provided with a thin film write element and a magnetoresistive (MR) read element. MR read elements, which are not dependent upon the speed relative to the magnetic disk, are capable of achieving a high degree of resolution. An MR read element includes a first shield film, a second shield film and an MR element. The first shield film and the second shield film are provided over a distance from each other via an appropriate nonmagnetic insulator and the MR element is provided between the first shield film and the second shield film.
The write element, which is constituted of an inductive electromagnetic transducer, is laminated on the MR read element. An inductive thin film magnetic transducer to constitute the write element is provided with a lower magnetic film which also functions as the second shield film for the MR read element, an upper yoke, a gap film, a coil film supported by an insulating film and the like.
The front ends of the lower magnetic film and the upper yoke are respectively constituted of a lower pole portion and an upper pole portion that face opposite each other over the gap film having a very small thickness, and a write operation is performed at the lower and upper pole portions. The lower magnetic film and an upper magnetic film are linked with each other so that their yoke completes a magnetic circuit at a back gap portion located on the opposite side from the lower and upper pole portions. The coil film is formed winding around the linking area of the yoke in a coil.
In order to support high recording density using this type of thin film magnetic head, the quantity of data stored per unit area of the magnetic disk (areal density) must be increased. An improvement in the areal density is achieved by improving the performance of the magnetic recording medium such as a magnetic disk and increasing the frequency at the write circuit as well as by improving the capability of the write element.
In one of the means for increasing the areal density by improving the capability of the write element, the gap length between the pole tips is reduced. However, since a reduction of the gap length leads to a reduction in the recording magnetic field intensity between the pole tips, there is naturally a limit to the degree to which the gap length can be reduced.
In another means for increasing the areal density, the number of data tracks that can be recorded on the magnetic disk is increased. The number of tracks that can be recorded on a magnetic disk is normally expressed as TPI (tracks per inch). The TPI capability of a write element may be enhanced by reducing the size of the head that determines the width of the data tracks. The head size is normally referred to as the head track width.
In the case of a conventional thin film magnetic head in the prior art described above, since the lower magnetic film at the write element is also employed as the second shield film of the MR read element, the width of the lower pole portion cannot be reduced, and consequently, a rather large side fringing magnetic field is generated during a recording operation. This magnetic field is caused by a leak of magnetic flux from the upper pole portion whose width is reduced to the lower magnetic film whose width is not reduced. Such a side fringing magnetic field restricts the lower limit of width that can be achieved and limits the degree to which the track density can be improved. In addition, it degrades the off-track performance when track data that have been written are read by the MR element.
As a means for eliminating the problem discussed above, Japanese Unexamined Patent Publication No. 262519/1995 and Japanese Unexamined Patent Publication No. 225917/1995 disclose a means for adjusting the width of the lower pole portion to the width of the upper pole portion through ion beam milling. However, the publications on the known art mentioned above only disclose the technology for improving the areal density by reducing the width of the pole tip at the write element and they do not disclose a structure of a thin film magnetic head that achieves an outstanding performance in recording data to a magnetic recording medium having a high degree of coercivity.
In addition, U.S. Pat. No. 5,600,519 discloses a structure provided with a tapered portion between the zero throat point and an expanded portion at the lower magnetic film and the upper magnetic film. However, the publication does not disclose how the write capability can be assured at the pole tips beyond the zero throat points.
Furthermore, U.S. Pat. No. 5,452,164 discloses a structure achieved by setting the width of the upper yoke to be larger than the width of the upper pole portion so that the two side surfaces of the upper yoke in the widthwise direction project out from the two side surface of the upper pole portion. However, this publication on the prior art technology does not disclose a means for preventing magnetic recording from occurring due to the magnetic flux leaking through the two side surfaces of the upper yoke in the widthwise direction.